Display screens with touch function in prior art have become the main stream in the display field due to their characteristics such as simple structure, light weight, thin thickness and low cost.
Touch screens mainly include capacitive touch screens, resistive touch screens and optical touch screens. Capacitive touch screens are popular and commonly used touch screens.
The touch principle of a capacitive touch screen will be described briefly below with respect to the structure of a touch screen.
FIG. 1 is a top schematic diagram of a capacitive touch screen including touch driving electrodes 800 disposed transversely and touch sensing electrodes 900 disposed vertically with mutual capacitances Cm generated by coupling between adjacent touch driving electrodes 800 and touch sensing electrodes 900. When a finger touches the screen, the touch of the finger will change the value of the mutual capacitance Cm. The location of finger touch is detected by detecting change of a current corresponding to the capacitance Cm before and after touch by a touch detection device. The finger changes the value of the mutual capacitance Cm by changing electric field between the touch driving electrode 800 and the touch sensing electrode 900.
Referring to FIG. 2 that is a schematic cross section of the touch driving electrode 800 and the touch sensing electrode 900 shown in FIG. 1, when a voltage is applied to the touch driving electrode 800 and the touch sensing electrode 900, an electric field is formed between them. In FIG. 2, the electric field line is denoted by the line segment with arrow. The electric field formed between the touch driving electrode 800 and the touch sensing electrode 900 includes two components, that is, a forward electric field formed between opposed overlapping surfaces of the touch driving electrode 800 and the touch sensing electrode 900 and a projection electric field formed between non-overlapping surfaces (in the present invention, overlapping surface refers to the overlapping surface formed by orthogonal projections of the touch driving electrode and the touch sensing electrode in the same plane). A finger can only change the value of mutual capacitance Cm by changing electric field projected outside the touch driving electrode 800 and the touch sensing electrode 900. The forward electric field is adverse to improving touch effect of the touch screen. The lager the area of the touch sensing electrode, the larger the projection electric field between the touch sensing electrode and the touch driving electrode, but at the same time, the larger the forward electric field between the touch sensing electrode and the touch driving electrode. When a large mutual capacitance is formed between directly opposed electric fields, large detection initial value of the touch detection device will be caused. It is impossible to accurately detect slight change of the projection electric field after the finger touches the touch screen, hence leading to poor touch effect of the touch screen.